Fix compatibility with pgf-3.1.4

Using dev-texlive/texlive-pstricks-2017 with >=dev-tex/pgf-3.1.4 fails:
  ...
  (/usr/share/texmf-site/tex/generic/pgf/utilities/pgffor.code.tex
  Runaway argument?
  ] {pgffor.code.tex}
  ! Paragraph ended before \ProvidesPackageRCS@i was complete.
  <to be read again>
                     \par
  l.11

The argument format for \ProvidesPackageRCS has changed in pgf and
pstricks provides its own version of the macro which isn't compatible
with the changes. Fix this by updating the provided macro and pgf
loading with the code from texlive-pstricks-2019.

Bug: https://bugs.gentoo.org/691828
Link: https://tex.stackexchange.com/questions/469005/pstricks-newly-introduced-error-in-package
Signed-off-by: Alexander Miller <alex.miller@gmx.de>

--- a/texmf-dist/tex/generic/pstricks/pstricks.tex
+++ b/texmf-dist/tex/generic/pstricks/pstricks.tex
@@ -130,14 +130,15 @@
   \XKV@tempa
 }
 %
-\def\ProvidesPackageRCS{\@ifnextchar[\ProvidesPackageRCS@i{\ProvidesPackageRCS@i[] }}  %$
-\def\ProvidesPackageRCS@i[#1] $#2${} %$
+\def\ProvidesPackageRCS#1{\typeout{Loading #1}}%
 \catcode`\@=\PstAtCode\relax
 \ifx\PSTFPloaded\endinput\else   \input pst-fp.tex\fi
 %
-\@ifundefined{pgfutil@empty}{\input pgfutil-common.tex}{}
-\@ifundefined{pgkeys@empty}{\input pgfkeys.code.tex}{}
-\@ifundefined{pgffor@emptyvalues}{\input pgffor.code.tex}{}
+\ifx\pgfkeysloaded\relax\else
+  \input pgfutil-common.tex
+  \input pgfkeys.code.tex
+  \input pgffor.code.tex
+\fi
 \let\pgfforeach\foreach
 %
 \def\fileversion{2.73}